1. Field of the Invention
The present invention relates to an ink jet head.
2. Description of the Related Art
A typical ink jet head is formed with a plurality of pressure chambers in fluid communication with a common ink chamber. The common ink charter is supplied with ink from an ink tank and distributes the ink to the pressure chambers. Pressure is applied to ink in selected ones of the pressure chambers to eject ink droplets from nozzles orifices that are in fluid communication with the pressure chambers.
A pressure wave is generated when pressure is applied to ink in one of the pressure chamber. The pressure wave can propagate into the common ink chamber. The resultant pressure fluctuations in the common ink chamber can adversely influence subsequent ink ejections, resulting in poor recording quality.
Ink jet printers are typically provided with a recovery unit. The recovery unit is used to remove dust or other material that might or does clog up channels or nozzle orifices. By providing and using the recovery unit, the ejection characteristics of the ink jet head can be maintain at a stable condition, or the ink jet head""s ejection characteristics can be recovered when the ink jet head starts ejecting ink in a defective manner.
One type of recovery unit includes a cap connected to a suction pump. When the recovery unit is operated, the cap covers the nozzle plate of the ink jet head and the suction pump generates a negative pressure within the cap. As a result, ink is sucked from the ink jet head through the cap. Bubbles generated in the ink jet head and ink that has started to dry up in the nozzle orifices are sucked out from the ink jet head along with the ink. However, this configuration has a disadvantage in that all of the ink in the common ink chamber and a portion of the ink in the ink tank are sucked into the cap, so that a relatively large amount of ink is consumed.
Another type of recovery unit is configured by connecting the ink tank to both opposite ends of the common ink chamber by tubes. Ink is forced through one of the tubes from the ink tank to the common ink chamber and through the other tube from the common ink chamber to the ink tank. This circulation operation removes bubbles from inside the common ink chamber and the tubes. This configuration uses up less ink than a recovery unit that sucks ink from the ink jet head into a cap. However, because the two tubes must be connected to either end of the common ink chamber, the structure of the ink jet head is complicated and also bulky.
A filter is typically provided where the common ink chamber is connected to the ink tank. The filter prevents dust and other debris from entering the pressure chambers and the nozzle orifices from the ink tank. However, sometimes debris can enter the ink jet head while the ink jet head is being manufactured. Such debris cannot be removed by the filter and so can clog up the pressure chambers and the nozzle orifices.
In order to absorb any pressure fluctuations in the common ink chamber, it is conceivable to form the portion of the common ink chamber where the common ink chamber is connected to the pressure chambers from a soft film, made from rubber, resin, or other soft material. However, it would be difficult to manufacture an ink jet head with a soft film mounted on a portion of the ink jet head. Additionally, portions of the pressure chamber row that are adjacent to the film have a different mechanical stiffness than do other portions of the pressure chamber row. When the mechanical stiffness of the pressure chambers lacks uniformity, pressure generated in the pressure chambers can also vary so that ink ejection also lacks uniformity
It is an objective of the present invention to provide a simple configuration that effectively absorbs pressure fluctuations associated with ink ejection so that cross talk can be prevented, uniform ink ejection from all of the pressure chambers can be assured, and high-quality images can be formed.
It is another objective of the present invention to provide a compact and simple configuration that enables stably maintaining and recovering good ejection characteristics of an ink jet head without unnecessarily wasting a great amount of ink.
It is still another objective of the present invention to overcome the above-described problems and to provide an ink jet head with a simple structure that reduces the amount of clogging in pressure chambers and nozzle orifices caused by dust and other debris that entered the ink jet head during production of the ink jet head.
To achieve the above-described objectives, an ink jet head according to a first aspect of the present invention includes a pressure chamber portion and a common ink chamber portion. The pressure chamber portion is formed with a row of pressure chambers aligned in a pressure chamber row direction. Each pressure chamber has a nozzle end and a common-ink-chamber end at opposite ends thereof. The nozzle end of each pressure chamber is in fluid communication with a corresponding nozzle orifice. The common ink chamber portion is formed with a common ink chamber elongated in the pressure chamber row direction. The common ink chamber includes a pressure-chamber region and a weak-mechanical-stiffness region that are separated from each other. The pressure-chamber region is in fluid communication with the common-ink-chamber end of each pressure chamber so that ink is supplied from the common ink chamber to the pressure chambers. The weak-mechanical-stiffness region has a weaker mechanical stiffness than mechanical stiffness at the pressure-chamber region. According to the present invention, mechanical stiffness is expressed using the following equation:
mechanical stiffness=dV/P
wherein P is the pressure applied in the common ink chamber; and
dV is the resultant fluctuation in volume in the common ink chamber. It can be understood that a larger value of mechanical stiffness actually represents a weaker mechanical stiffness.
With this configuration, pressure fluctuations are absorbed by the region with weak mechanical stiffness. Also, all the pressure chamber have uniform mechanical stiffness so that pressure generated in the pressure chambers is uniform and good-quality recording can be realized.
According to a second aspect of the present invention, an ink jet head includes a pressure chamber portion and a common ink chamber portion. The pressure chamber portion is formed with a row of pressure chambers aligned in a pressure chamber row direction. Each pressure chamber has a nozzle end and a common-ink-chamber end at opposite ends thereof. The nozzle end of each pressure chamber is in fluid communication with a corresponding nozzle orifice. The common ink chamber portion is formed with a common ink chamber elongated in the pressure chamber row direction. The common ink chamber includes a pressure-chamber region, an ink-supply-connection opening, and a broad-width region. The pressure-chamber region is located where the common ink chamber is in fluid communication with the common-ink-chamber end of each pressure chamber, so that ink is supplied from the common ink chamber to the pressure chambers. The ink-supply-connection opening is in fluid communication with an external ink supply source. The broad-width region is located at an opposite lengthwise end of the common ink chamber than the ink-supply-connection opening. The broad-width region is separated from the pressure-chamber region and has a broader width than other regions of the common ink chamber.
Pressure waves are generated when the pressure chambers operate to eject ink. The pressure waves can propagate into the common ink chamber in association with ink flow. With the configuration of the second aspect of the present invention, pressure waves that propagate into common ink chamber are dampened by the broad-width region. Therefore, pressure fluctuations in the common ink chamber can be reduced and ink ejection characteristics can be stabilized.
An ink jet head according to a third aspect of the present invention includes a pressure chamber portion, a common ink chamber portion, and a circulation channel portion. The pressure chamber portion is formed with a row of pressure chambers aligned in a pressure chamber row direction. Each pressure chamber has a nozzle end and a common-ink-chamber end at opposite ends thereof. The nozzle end of each pressure chamber is in fluid communication with a corresponding nozzle orifice. The common ink chamber portion is formed with a common ink chamber elongated in the pressure chamber row direction. The common ink chamber is in fluid communication with the common-ink-chamber end of each pressure chamber so that ink is supplied from the common ink chamber to the pressure chambers. The common ink chamber includes an ink-supply-connection opening at one lengthwise end thereof to enable connection to an external ink supply. The circulation channel portion is formed with a circulation channel that extends substantially parallel with the common ink channel. The circulation channel includes an ink-supply-connection opening at one lengthwise end thereof to enable connection to the external ink supply. The circulation channel and the common ink chamber are in fluid communication with each other at a lengthwise end opposite from the lengthwise end formed with the ink-supply-connection openings of the circulation channel and the common ink chamber.
With this configuration, ink can be supplied into the ink-supply-connection opening of one of the circulation channel and the common ink chamber and discharged through the ink-supply-connection opening of the other one of the circulation channel and the common ink chamber. As a result, air bubbles in the ink can be returned to the ink supply source along with the ink, so that ink supplied from the common ink chamber to the pressure chambers has less air bubbles. Accordingly, a compact and simple configuration that enables stably maintaining and recovering good ejection characteristics of an ink jet head without unnecessarily wasting a great amount of ink can be made.
The ink jet head according to any of the first to third aspects of the present invention can be provided to a ink jet recording device with a circulation unit. The circulation unit is in fluid communication with the ink-supply-connection opening of the common ink chamber and with the ink-supply-connection opening of the circulation channel. The circulation unit forces ink from the ink supply source into one of the ink-supply-connection openings and returns ink to the ink supply source from the other one of the ink-supply-connection openings.
An ink jet head according to a fourth aspect of the present invention includes a first substrate, a second substrate, and a third substrate stacked on top of each other. The first substrate is formed with a plurality of pressure chambers aligned in a pressure chamber row direction. Each pressure chamber has a nozzle end and a common-ink-chamber end at opposite ends thereof. The nozzle end of each pressure chamber is in fluid communication with a corresponding nozzle orifice. The second substrate is formed with a common ink chamber elongated in the pressure chamber row direction. The common ink chamber is in fluid communication with the common-ink-chamber end of each pressure chamber so that ink is supplied from the common ink chamber to the pressure chambers. The third substrate is interposed between the first substrate and the second substrate. The third substrate includes a plurality of filter holes located where the common ink chamber is in fluid communication with the common-ink-chamber end of each pressure chamber.
With this configuration, because the filter holes are interposed between the pressure chambers and the common ink chamber, dust and other debris that entered the ink jet head during manufacture of the ink jet head is less likely to flow from the common ink chamber into the pressure chambers and accumulate in the channel between the common ink chamber and the pressure chamber. Accordingly, clogs in the pressure chambers and the nozzle orifices can also be prevented. Also, the filters can be easily provided to all of the pressure chambers by sandwiching the third substrate, which is formed with the filter holes, between the first substrate, which is formed with the pressure chambers, and the second substrate, which is formed with the common ink chamber.